# OCR A-Level Physics/Glossary of Terms

Definitions of keywords and terms that you will need to know.

## A[edit]

- Absolute zero
- Zero on the thermodynamic temperature scale, or 0 K (kelvin), where a substance has minimum internal energy, and is the coldest possible temperature. It is equal to -273.15 degrees Celsius.
- Absorption spectrum
- A spectrum of dark lines across the pattern of spectral colours produced when light passes through a gas and the gas absorbs certain frequencies depending on the elements in the gas.
- Acceleration
- The (instantaneous) rate of change of velocity in respects to time.
- Acceleration of free fall (g)
- The acceleration of a body falling under gravity (9.81ms
^{-2}on earth). - Ammeter
- A device used to measure the electric current in a circuit. It is connected in series with the components.
- Amount of substance
- A SI quantity, measured in moles (mol).
- Ampere
- The SI unit for electric current.
- Amplitude
- The maximum displacement of a wave from its rest/mean position (measured in metres).
- Antinode
- A point of maximum amplitude along a stationary wave caused by constructive interference.

## B[edit]

## C[edit]

- Coulomb's Law
- The force between two charges is directly proportional to the product of the charges and inversely proportional to the distance between them squared
- Couple
- Two equal, opposite and parallel forces which create rotational force.

## D[edit]

- Displacement
- A vector quantity, the distance of an object from its initial position, in a given direction
- Density
- Density is the mass of a body per unit volume
- Decay Constant
- The probability of decay of a nucleus per unit time

## E[edit]

- Electric field strength (E)
- The force that a unit charge would experience at a specified point. Measured in Volts per metre or Newtons per Coulomb
- Electric potential (V)
- The energy that a unit charge would have at a specified point. Measured in Volts
- Energy
- The stored ability to do work
- Extension (x)
- The change in length of an object when a force is applied to it

## F[edit]

- Faraday's Law
- The emf induced in a conductor is directly proportional to the rate at which the magnetic flux changes.
- Force
- A force causes a mass to change motion

- Frequency
- The number of waves that pass a fixed point in a unit of time

## G[edit]

- Gravitational Field Strength (g)
- The force that a unit mass would experience at a specified point. Measured in metres per second per second or Newtons per kilogramme
- Gravitational Potential
- The energy that a unit mass would have at a specified point. Measured in Joules per kilogramme
- Gravitational Potential Energy
- the energy an object has due to its relative position above the ground. Found by mass x gravity (or gravitational field strength) x height
- or force per unit mass at a set point in a gravitational field

## H[edit]

- Heat
- is a form of energy transfer, also known as 'Thermal Energy'.

- Hooke's Law
- an approximation that states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit.

## I[edit]

- Instantaneous acceleration
- acceleration at a specific time; slope of tangent to velocity- time graph.

- Instantaneous position
- position of an object at specific time.

- Instantaneous velocity
- slope of the tangent to position- time graph.

## J[edit]

- Joule
- The SI unit of work done, or energy. One joule is the work done when a force of one newton moves an object one metre.

## K[edit]

- Kinetic Energy
- The energy an object possesses due to its motion, given by KE = 0.5 x mass x velocity²

## L[edit]

- Lenz's Law
- An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

## M[edit]

**Magnetic Flux**

Magnetic flux is the product of magnetic flux density and the projection of area onto a surface at right angles to the magnetic field

## N[edit]

- Newton
- Unit in which force is measured. Symbol "N". One Newton is the force required to give a mass of 1kg an acceleration of 1ms^-2

## O[edit]

## P[edit]

- Period (T)
- The time taken for one complete oscillation. Denoted by 'T'. T=1/f

- Power
- The rate at which work is done.
- Pressure
- The load applied to an object per unit surface area.

- Potential difference
- The work done in moving a unit positive charge from one point to the other. The unit is volt.

## Q[edit]

- Q or q
- Often used as the symbol for charge in equations

## R[edit]

- Resistivity
- The property of a material that measures it resistance to electric current. It is defined as the resistance a wire of the material would have if it had a cross sectional area of one metre square and a length of one meter.

- Radian
- A radian is the angle subtended at the centre of the circle when the arc length is equal in length to the radius.

## S[edit]

- Scalar
- A quantity with magnitude but no direction.

- Speed
- A scalar quantity, speed = distance / time

* NB* s can also mean displacement.

- Stopping Distance
- Stopping distance = Thinking distance + Braking distance
- thinking distance (distance traveled while reacting) = time taken to react X velocity
- braking distance (distance traveled while braking)

## T[edit]

- Temperature
- A SI quantity, measured in kelvin (K).
- Tensile force

The forces being applied onto a material (usually a wire) on two opposite sides in order to stretch it. Both forces' values are the same as the tensile force value.

- Tensile stress
- The tensile force per unit cross-sectional area.
- Terminal Velocity
- maximum velocity a body can travel. When resistive forces = driving force, acceleration = 0, so it cannot travel any faster.
- Thermistor
- An electrical component that changes its resistance depending on its temperature.
- Thinking distance
- The distance travelled from seeing the need to stop to applying the brakes.
- Threshold frequency
- The lowest frequency of electromagnetic radiation that will result in the emission of photoelectrons from a specified metal surface.
- Thrust
- A type of force due to an engine (usually forward force).
- Time interval (t)
- A SI quantity, measured in seconds (s).
- Torque / moment
- Moment = force x perpendicular distance from the pivot to the line of action of the force
- Torque = one of the forces x the distance between them

- Transverse Wave
- A progressive wave that transfers energy as a result of oscillations/vibrations.
- Triangle of forces
- If three forces are acting at a point that can be represented by the sides of a triange, the forces are in equilibrium.
- Turning forces
- More than one forces that if unbalanced will cause a rotation.

## U[edit]

- Ultimate tensile strength
- The maximum tensile force that can be applied to an object before it breaks.
- Ultimate tensile stress
- The maximum stress that can be applied to an object before it breaks.
- Ultraviolet
- A form of electromagnetic wave (wavelengths 10
^{-9}-3.7x10^{-7}m). It may cause sun tanning. Usually classified into three categeries:UV-A, UV-B and UV-C. - Upthrust
- A force experienced due to the pressure difference of the fluid at the top and bottom of the immersed portion of the body.

## V[edit]

- Vector
- A quantity with magnitude and direction.
- Velocity
- The (instantaneous) rate of change of displacement with respect to time. Velocity is a vector.
- Velocity-time graph
- A motion graph which shows velocity against time for a given body.
- Volt (V)
- The unit of potential difference (p.d.) or electromotive force (e.m.f.)

potential difference=energy/charge

- Voltmeter
- A device used to measure the potential difference across a component. It is connected in parallel across a component.
- Volume(V)
- A physical quantity representing how much 3D space an object occupies, measured in cubic metres(m
^{3})

## W[edit]

- Watt(W)
- The unit of power.

- power = energy / time
- Wave
- Series of vibrations that transfer energy from one place to another.
- Wavelength(λ)
- The smallest distance between one point of a wave and the identical point of the next wave, measured in metres (m).
- Wave-particle duality
- The theory which states that all objects can exhibit both wave and particle properties.
- Weight
- The gravitational force acting on a body, measured in newtons (N).

weight=mass x gravitational force

- Work Done
- The energy transferred when an object is moved through a distance by a force. Can be calculated by multiplying the force involved by the distance moved in the direction of the force.

Alternatively, [work done = transfer of energy]. i.e., work is done when energy is transferred from one form to another. [OCR do not accept this definition if asked "Define work done by a force"]

- Work function energy (Φ)
- The minimum energy that is required for a material to release an electron, measured in joules(J).

## X[edit]

- X rays
- A form of electromagnetic wave (wavelengths:10
^{-12}-10^{-7}m). It is used in X-ray photography.

## Y[edit]

- Young's double slit experiment
- An experiment to demonstrate the wave nature of light via superposition and interference.
- Young Modulus
- Stress per unit Strain, units: Pascals or N/m
^{2}